1. Technical Field
The present invention relates generally to footwear and more particularly to athletic-type shoes having a spring assembly module integrated into the sole and/or heel of a shoe for cushioning the impact forces placed thereon.
2. Discussion
As is generally known in the art, footwear is currently comprised of a sole made of foam, plastic, rubber, or leather in various forms and densities. A manufactured upper made of nylon fabric, plastic or leather in various combinations is then attached to the sole. As the wearer of the shoe walks, jogs, or runs in the shoe, the harder plastics and foams forming the sole give the shoe shape and support while the softer foams give comfort and absorb the shock of the foot pounding onto the hard surfaces of a court, street, or sidewalk. As the foam absorbs the impact energy from the walking or running forces, it converts some of that energy into shape deformation. Most of the remaining energy is converted into heat. Thus, the temperature inside the shoe can easily exceed 130.degree. F. As the foot gets hot, the body tries to manage the excess heat and the foot sweats. The sweat contains moisture, salt, ammonia and other chemicals that, together with the heat, attack and degrade the plastics, foams and rubber components of the shoe.
Additionally, the foam takes an increased set with more use resulting in less effectiveness in absorbing the impact forces. It is commonly recommended that shoes be used every other day to give the shoes a chance to dry out and for the foam to regain its shape, though the shape will never return entirely. Shoe manufacturers also recognize that the shoe's capability to absorb shock can be seriously degraded after only 100 miles of hard running.
In an attempt to overcome this problem, air bags or air bladders of various shapes have been used with some success to absorb shock and provide additional comfort. The currently used air bags are able to return more energy to the wearer through a higher rebound rate thereby converting less energy to heat. However, these air bags are also made of plastic which is susceptible to degradation problems resulting from the heat and chemical attack of the operating environment. As they degrade, air bags lose air and their strength. Air bags also have less stability as the air "squirts" away from the impact load requiring additional means of support to be utilized by designers to provide more stability to the shoe.
Accordingly, it is desirable to provide a device for absorbing the impact forces imparted on footwear which is lightweight and less sensitive to the destructive effects of heat and chemicals within the operating environment. It is further desirable to provide an impact absorbing device which does not break down structurally with extended use, and is further capable of returning a higher level of energy to the wearer during a walking or running activity.